The present invention relates to a power generator that generates power by supplying fuel gas to the fuel electrode of a fuel cell.
The fuel cell is made up of a fuel electrode and an air electrode with an electrolyte present therebetween. Power is generated by supplying fuel gas and the like to the fuel cell. A solid oxide fuel cell (SOFC) in particular is structured as an assembly of an electrolyte made of a solid oxide, a fuel electrode (hydrogen pole), and an air electrode (oxygen pole), the electrodes being assembled with the electrolyte through bonding or the like. The solid oxide fuel cell can generate high output power when fuel gas is supplied to the fuel electrode, while air and the like are supplied to the air electrode. The solid oxide fuel cell can use not only hydrogen gas but also a gas containing a large amount of carbon monoxide (e.g., exhaust gas of vehicles, such as automobiles, driven with internal combustion engines) as fuel gas.
Such a solid oxide fuel cell is described in Patent Document 1. In this cell, the fuel electrode and the air electrode are exposed to separate chambers, and hydrogen and oxygen are supplied in these separate chambers. The solid oxide fuel cell, which is structured to receive a supply of fuel and air in a separate manner to cause a reaction, is called a double-chamber type cell. The solid oxide fuel cell, which is structured to receive a supply of fuel and air through the same flow channel to cause a reaction, is called a single-chamber type cell.
In both the above-described solid oxide fuel cells of the double-chamber type and the single-chamber type, a gas flow channel is formed along the electrodes. The flow channel is covered with a wall made of a highly electroconductive material to collect current. However, in the case of using exhaust gas, low-concentration fuel needs to be supplied in a large amount, which necessitates increase in the volume of the gas flow channel. However, when the gas flow channel is enlarged, a contact area of the gas with the electrode decreases, which results in an increased current collection (electric) resistance.
Accordingly, there is known a current collection technology that enlarges a contact area of the fuel while securing a gas flow channel by providing a porous body in the gas flow channel instead of covering the gas flow channel with a wall, the porous body being made of a porous metal or an oxide material (e.g., foaming nickel) having a high electrical conductivity. However, the solid oxide fuel cell generates power by using oxygen in the air and the fuel at high temperatures (for example, 700° C. to 1000° C.). To use oxygen in such high-temperature environments, a material high in oxidation resistance needs to be selected as a porous body. Materials having a high oxidation resistance at high temperatures are expensive and high in specific gravity. As a result, it is difficult to make these materials porous, foamed, and the like.